The present invention relates to a remaining-capacity dispersion detecting apparatus for detecting a dispersion state in remaining capacities of respective cells constituting a battery pack and a remaining-capacity control apparatus for controlling the remaining capacities of cells.
In an electric vehicle that runs by using a motor (battery) or a hybrid vehicle that runs by using two of motor and internal combustion engine, a battery pack (assembled battery) including a plurality of cells (capacitors or single batteries) connected in series with or in series-parallel with each other is used as a power-source for driving the motor provided to drive the vehicle. Note that the above-mentioned battery pack in explanations according to the present invention also implies a plurality of capacitors connected in series with or in series-parallel with each other. In such battery pack, a dispersion in remaining capacities (i.e., charging rate or state of charge) of respective cells is caused based on differences in self-discharge, deterioration, and internal resistance of each cell when leaving the battery pack for a long time, e.g., for a few months. When the dispersion in remaining capacities of respective cells has occurred, usable electric power of battery pack is restricted. Hence, it is necessary to suppress the dispersion in the remaining capacities as far as possible. Accordingly, a processing for adjusting the dispersion in remaining capacities (equalizing the remaining capacities, i.e., charging rates) is carried out by detecting the dispersion in remaining capacities.
In the case where the above-mentioned dispersion of remaining capacities is detected, if the dispersion of remaining capacities is detected when the battery pack is under a loaded condition where the battery pack is supplying electric power to a load, voltage and current vary according to a variation of the load. Thereby, it is difficult to accurately detect the dispersion in remaining capacities of respective cells. Therefore, a published Japanese Patent Application No. 2004-297852 discloses a previously-proposed processing for detecting the dispersion in remaining capacities on the basis of a voltage (i.e., open voltage) at the time of activation (at the time of no-load).